Aluminum base alloys

ABSTRACT

The disclosure teaches improved aluminum base alloys containing silicon, magnesium, chromium and zirconium. The alloys have a combination of high strength and high impact properties.

United States Patent 91 Sperry et al.

[ 51 Feb. 20, 1973 [54] ALUMINUM BASE ALLOYS [75] Inventors: Philip R. Sperry, North Haven; Damian V. Gullotti, Madison, both of Conn.

[73] Assignee: Olin Corporation [22] Filed: Oct. 28, 1971 [21] Appl. No.: 193,458

Related [1.8. Application Data [63] Continuation-in-part of Ser. No. 14,189, Feb. 25,

1970, Pat. No. 3,642,542.

[52] US. Cl. ..l48/32.5, 148/127 [51] Int. Cl ..C22c 21/02 [58] Field of Search ..l48/32, 32.5, 11.5 A, 12.7,

'[56] References Cited UNITED STATES PATENTS 3,113,052 12/1963 Schneck. ..l48/11.5 A 3,234,054 2/1966 Sperry ..148/1 1.5 A

Primary Examiner-Richard 0. Dean Att0meyRobert H. Bachman et al.

[57] ABSTRACT The disclosure teaches improved aluminum base alloys containing silicon, magnesium, chromium and zirconium. The alloys have a combination of high strength and high impact properties.

10 Claims, 1 Drawing Eigure PA-IENIEnsem-ma 7 1 T351 2 ALLOV- B ALLOV K BROKEN CHARPV IMPACT TEST SPEC/MENSWMAGN/F/CAT/ON OF 2.5 X MACRO-ETCHED AFTER IMPACT TEST/N6 7'0 SHOW GRAIN STRUCTURES.

INVENTORS PHIL/P R. SPERRY DAM/AN l. GULLOTT/ ZMMZMM ATTORNEY ALUMINUM BASE ALLOYS CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION The present invention relates to improved aluminum base alloys containing silicon and magnesium, wherein said alloy is a hot worked alloy and has high strength and high impact properties.

Hot worked aluminum base alloys containing magnesium and silicon find wide application in a wide variety of uses, for example, they may be readily used as extrusions, forgings or rolled products.

There are many applications where it is highly desirable to develop a hot worked product having a combination of high strength and high impact properties. For example, there are certain applications for aluminum alloy extrusions where high impact strength is one of the major requirements. A highway bridge railing or median barrier of extruded aluminum must absorb a considerable amount of energy from a vehicle crashing into it before it fails.

Accordingly, it is a principal object of the present invention to provide new and improved hot worked aluminum base alloys.

It is a further object of the present invention to provide improved hot worked aluminum base alloys having a combination of high strength and high impact properties.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily obtained.

SUMMARY OF THE INVENTION The improved alloy of the present invention consists essentially of silicon from 0.3 to 1.3 percent, magnesium from 0.3 to 1.5 percent, chromium from 0.03 to 0.40 percent, and zirconium from 0.03 to 0.20 percent, balance essentially aluminum, wherein substantially all grains are fibrous and grossly elongated, with a length to thickness ratio as extruded of at least to l, and preferably 100 to 1. In the preferred embodiment, the alloy of the present invention also contains manganese in an amount from 0.03 to 0.40 percent, with the total chromium plus zirconium plus manganese content being preferably from 0.2 to 0.35 percent.

The improved alloy of the present invention is a hot worked product and has a surprising combination of high strength and high impact properties. As indicated hereinabove, the microstructure is a substantially unrecrystallized grain structure, and, significantly, substantially all grains are fibrous and grossly elongated, with a length to thickness ratio as extruded of at least 10 to l. The elongated grains contain a plurality of subgrains which are visible under high magnification. In addition, the chromium and zirconium additions, and manganese when present, are at least partly present in a uniform dispersion precipitated throughout the matrix. It is particularly surprising in accordance with the present invention that the alloy of the present invention achieves such excellent properties.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing which forms a part of the present specification is a photograph at a magnification of 2.5X comparing an impact specimen of the alloy of the present invention with a conventional material. The drawing will be discussed in more detail hereinbelow.

DETAILED DESCRIPTION The improved alloy of the present invention is preferably processed in accordance with the following procedure: hot working the alloys at a finishing temperature in excess of 850F; water quenching the alloys down to a temperature of 350F or below at a cooling rate of from 1,000 to l0,000F per minute; and thermally artificially aging the alloys at a temperature from 0 200 to 410F for from 15 minutes to 24 hours.

As stated hereinabove, the alloys of the present invention are characterized by a surprising combination of high strength and high impact toughness. For example, generally the minimum properties obtained in accordance with the foregoing process are as follows: tensile strength at least 38,000 psi; yield strength at 0.2 percent offset at least 35,000 psi and elongation at least 8 percent.

The minimum impact toughness of the alloys of the present invention is for a Va inch thick specimen, the Charpy V-Notch impact test yields at least 15 foot pounds. One would obtain at least 20 foot pounds for a 0.394 inch thick specimen, and typically 30 to 40 foot pounds.

In addition to the foregoing the alloy of the present invention has numerous other highly desirable characteristics, for example, it is easily extruded and has good corrosion resistance.

The alloy of the present invention contains from 0.3 to 1.3 percent silicon and preferably from 0.4 to 0.9 percent silicon. Silicon in the preferred range has been found to give particularly advantageous results. The alloy of the present invention contains magnesium in an amount from 0.3 to 1.5 percent and preferably from 0.4 to 1.0 percent. The chromium content may vary from 0.03 to 0.40 percent and preferably from 0.05 to 0.35 percent. The zirconium may vary from 0.03 to 0.20 percent and preferably from 0.05 to 0.15 percent.

As stated hereinabove, it has been found to be particularly advantageous to include manganese in an amount from 0.03 to 0.4 percent and preferably in an amount from 0.05 to 0.3 percent.

Other especially advantageous additives are titanium up to 0.10 percent and vanadium up to 0.15 percent.

Naturally, the present invention contemplates conventional impurities common for alloys of this type. This is important since it indicates that the improved properties of the alloys of the present invention are obtainable with normal commercial purity materials. For example, normal impurities include 0.60 percent maximum iron; 0.30 percent maximum copper, 0.50 percent maximum zinc; up to 0.008 percent boron; 0.10 percent maximum each of other elements the total of which is a maximum of 0.50 percent.

As stated hereinabove, the microstructure of the alloys of the present invention is particularly significant in obtaining the surprisingly improved properties of the alloys of the present invention. Substantially all grains are fibrous and grossly elongated, with a length to thickness ratio as extruded of at least to 1. This can be clearly seen from the drawing which forms a part of the present specification wherein the upper specimen represents an alloy of the present invention, showing an unrecrystallized, fibrous grain structure, with grossly elongated grains. The impact strength of this material was 55.8 foot pounds, and the material did not completely fracture. On the other hand, the material on the bottom shows a completely recrystallized grain structure and had a Charpy impact strength of 10.8 foot pounds.

In addition, there are other aspects of the alloys of the present invention which are important in achieving their excellent properties. The grossly elongated grains contain a plurality of fine, substantially uniform subgrains or polygonized grain structure within each fibrous grain. These are visible under high magnification. Also, the precipitates formed by chromium, zirconium and manganese are favorably dispersed throughout the matrix. Thus, it can be seen that the alloys of the present invention consistently achieve high impact toughness together with other good physical characteristics due to their composition together with a highly advantageous microstructure.

The manner of melting and casting the alloy is not especially critical and conventional methods of melting and casting may be conveniently employed. It is desirable to uniformly distribute the silicon and magnesium throughout the matrix of the alloy before the process of the present invention is performed, such as by a homogenization heat treatment subsequent to the casting operation. Before or during hot working some high temperature precipitate should be formed due to Cr, Zr and Mn, as this is the mechanism by which recrystallization is inhibited. However, this can be accomplished by reheating for hot working as well as by homogenization.

After casting the alloy should be hot worked at a finishing temperature in excess of 850F and preferably in excess of 900F, for example, forging, rolling or extruding. By finishing temperature it is meant the final temperature at which significant deformation is obtained in the but working operation. When the alloy is extruded, the die exit temperature should be in excess of 850F. It is preferable that the actual temperature be high enough to dissolve substantially all Mg and Si which is available for maximum strengthening.

Following the hot working operation the material should be rapidly quenched to a temperature of at least 350F at a cooling rate of l,000 to l0,000F per minute. The rapid quenching is normally obtained by plunging the material in water or by passing the material through a water spray quench.

Optionally, the material may then be cold worked up to 5 percent, e.g., rolling, stretching, etc.

The material should be then artificially aged at a temperature of 200 to 4l0F for minutes to 24 hours.

The alloys of the present invention are quench sensitive. It is a particularly surprising finding of the present invention that this quench sensitivity can be controlled with respect to a particularly preferred composition.

This is accomplished by a critical adjustment of the quantities of chromium, zirconium and manganese prevent in the alloy so that each of these materials are present in an amount of 0.03 to 0.2 percent, and the total chromium plus zirconium plus manganese content is from 0.2 to 0.35 percent. It has been found that when the composition has been controlled in this manner, the alloy may be air cooled at a cooling rate from to 1,000F per minute, naturally with reasonable section thicknesses; otherwise, the alloy should be water quenched at the more rapid rate specified hereinabove.

The air cooling is normally achieved by using appropriately placed fans.

In this particularly preferred composition, the hot working step should be performed at a finishing temperature in excess of 900F and preferably in excess of 950F.

The alloy of the present invention and improvements resulting therefrom will be more readily apparent from a consideration of the following illustrative examples.

EXAMPLE I ingots were prepared by direct chill (DC) casting in a conventional manner summarized as follows. Melting and alloying was carried out in a gas-fired, open hearth furnace. After alloying the melt was degassed by gaseous chlorine fluxing for 20 minutes. The average pouring temperature was 1,370F. The average casting speed was 4 5% inch per minute and the metal head was maintained between 2 A and 3 inch. The composition of the alloys prepared are given in Table I below.

TABLE I Alloy A silicon 0.78 magnesium 0.47 iron 0.14 titanium 0.01 chromium 0.050 zirconium 0.056 manganese 0.054 copper 0.00 zinc 0.04 aluminum Balance Alloy B silicon 0.81 magnesium 0.53 iron 0.14 titanium 0.01 chromium 0.107 zirconium 0.108 manganese 0.108 copper 0.00 zinc 0.03 aluminum Balance EXAMPLE [I The alloys prepared in Example I were processed in the following manner. The ingots were given a homogenization heat treatment of about l,025F for about 10 hours followed by cooling in air. The billets were sawed to length and reheated for extrusion in a gas-fired, billet heater with control temperature set at 1,000F. Measured surface temperatures ranged between 975 and 1025F before entering the press. Three extrusion dies were used to produce section thicknesses of one-eighth, one-fourth, and one-half inch. Exit temperatures ranged from 980 to 1,000F. One extrusion of each thickness was fan cooled as it exited from the press at a cooling rate in the range of the process of the present invention; another was water quenched by passing it through an open ended trough fed by an upward flow of water at both ends at a cooling rate in the range of the process of the present invention. All extrusions were aged at room temperature for about 24 hours, followed by artificial aging at 350F for 5 hours. Tensile test specimens and Charpy impact specimens were taken from the extrusions. One-eighth and V4 inch thick extrusions were tested with reduced width from the standard 0.394 inch and the impact test value was corrected for reduced area.

The results are shown in Table 11 below and clearly show a combination of high strength and high impact properties.

The excellent improved impact toughness was .iue to the retention of an unrecrystallized grain structure in the alloys. The microstructure of both alloys was characterized by substantially all grains being fibrous and grossly elongated, with the length to thickness ratio being substantially greater than 25 to l. The elongated grains contained a plurality of fine, uniform sub-grains which were visible under high magnification. The precipitates formed by chromium, zirconium and manganese were favorably dispersed throughout the matrix. There were shallow layers of recrystallized grains at the extrusion surfaces. These shallow layers were shallower for Alloy B than for Alloy A, which had a smaller amount of chromium and zirconium and manganese.

TABLE II Elon- Section g 9" Charpy thickness Alloy Quench urs Y.S. (R81) I p (inches) Method (ksi) at 0.2% 2 1n.) Strength 4 A Fan 0501 43.5 41.0 20.5 Water 46.1 43.4 11 25.2 Va 8 Fan Cool 43.5 39.3 9.5 26.8 Water 45.5 42.4 10 26.8 A A Fan Cool 43.0 39.3 8 24.0 Water 46.0 43.1 9.5 27.8 14 B Fan Cool 41.3 36.5 9.5 35.2 Water 45.8 43.0 9.5 37.3 a A Fan c001 41.4 37.0 10.5 30.3 Water 44.0 41.0 11.5 58.0 as B Fan c001 38.5 33.3 12 69.5 Water 48.6 46.0 12.5 43.5

EXAMPLE III lngots were prepared in a conventional manner from two kilogram melts cast by the tilt mold (Durville) process. The resultant compositions are indicated in Table III below.

TABLE III Alloy C silicon 0.71 magnesium 0.56% iron 0.16% copper 0.0l% titanium 0.02% zirconium 0.16% aluminum Balance Alloy D silicon 0.83% magnesium 0.58% iron 0.20% copper 0.01% titanium 0.01% chromium 0.31% aluminum Balance Alloy E silicon 0.71% magnesium 0.57% iron 0.16% copper 0.0l% titanium 0.02% chromium 0.22%

zirconium 0.10% aluminum Balance Alloy F silicon 0.78% magnesium 0.58% iron 0.17% copper 0.01% titanium 0.02% chromium 0.10% manganese 0.09% zirconium 0.11% aluminum Balance EXAMPLE IV The alloys prepared in Example 111 were processed in the following manner. The ingots were homogenized at 1,025F for 12 hours. The ingots were hot rolled from 1,000F, 80% in one pass. The materials were quenched by plunging into water at room temperature, thus providing a cooling rate in the range of the process of the present invention. The materials were age hardened 5 hours at 350F. The materials were then tested for tensile properties and Charpy impact properties using ,4 inch specimens. The results are shown in Table IV below. The results clearly show that the alloy of the present invention, namely Alloys E and F gave surprising improved properties over comparative A1- Ioys C and D. It is noted that Alloy C does not contain the chromium addition and Alloy D does not contain the zirconium addition.

Comparative Alloys C and D were about percent recrystallized, with the recrystallized grains being substantially equiaxed. On the other hand, the microstructure of Alloys E and F was substantially as described in Example II, with the length to thickness ratio being in excess of 15 to I.

Table IV Charpy Impact lngots were prepared in a manner after Example have the composition indicated in Table V below.

Ito

TABLE V Alloy G silicon 0.84% magnesium 0.50% iron 0.20% copper 0.003% titanium 0.023% boron 0.004% Alloy H silicon 0. 8 l magnesium 0.58% iron 0.19% copper 0.004% titanium 0.023% chromium 0.25% zirconium 0.082 boron 0.004% Alloy I (Commercial Alloy AA 635) silicon 1.08% magnesium 0.65% iron 0.19% copper 0.004% titanium 0.024% manganese 0.66%

boron 0.004% Alloy .1 (Commercial Alloy 6061) silicon 0.64% magnesium 1.10% iron 0.25% copper 0.25% titanium 0.017% chromium 0.18% manganese 053% EXAMPLE VI The materials from Example V were processed in a manner after Example 1V except that the materials were hot rolled 50 percent in one pass rather than 80 percent and Alloys 1 and .1 were aged for 8 hours at 350F. The results are given in Table VI below and clearly show the surprising properties of Alloy H which represents the alloy of the present invention. It should be noted that the Charpy impact test utilized standard 0.394 inch specimens.

Alloy G was characterized by a completely recrystallized grain structure. Alloy H of the present invention was substantially as described in Example 11, with the length to thickness ratio being in excess of 10 to 1. A1- loys l and .1 were substantially unrecrystallized, with the length to thickness ratio being about 5 to 1. In addition, Alloys 1 and J lacked the favorably uniform dispersion of chromium or manganese.

TABLE VI Tensile Properties Alloy K was prepared in essentially the same manner as 111 Example land had the follow composition:

TABLE Vll Alioy K (Commercial Alloy AA 6061) silicon 0.68%

magnesium 0.93%

iron 0.39%

copper 0.22%

titanium 0.014%

chromium 0.05 8% manganese 0.13%

The alloy was extruded into a shape having a thickness of one-half inch using substantially the same procedure as outlined in Example 11, including a water quench as it exited from the extrusion press and an agingtreatment at 350F for 6 hours. Alloys K and B, in section thicknesses of one-half inch, were machined into Charpy V-Notch impact specimens and were impact tested. Alloy B of the present invention had a Charpy impact strength of 55.8 foot pounds, while Alloy K had a Charpy impact strength of 10.8 foot pounds. The broken impact specimens were then macro-etched to reveal the grain structure of the test pieces. The drawing, which forms a part of the present specification, shows Alloy B as the upper sample and Alloy K as the lower sample and is at a magnification of 2.5X. The

FIGURE compares the high impact energy, 55.8 foot ounds, and the fgrossly elongated, fibrous rain strucure of Alloy B o the present invention, wit the essentially recrystallized structure and low impact energy, 10.8 foot pounds, of Alloy K.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. A hot worked aluminum base alloy having high strength and high impact properties consisting essentially of silicon from 0.3 to 1.3 percent, magnesium from 0.3 to 1.5 percent, chromium from 0.03 to 0.40 percent, zirconium from 0.03 to 0.20 percent, balance essentially aluminum, wherein substantially all grains are fibrous and grossly elongated, with a length to thickness ratio as extruded of at least 10 to 1, wherein said elongated grains contain a plurality of sub-grains.

2. An alloy according to claim 1 containing silicon from 0.4 to 0.9 percent.

3. An alloy according to claim 1 containing magnesium from 0.4 to 1.0 percent.

4. An alloy according to claim 1 containing manganese from 0.03 to 0.4 percent.

5. An alloy according to claim 4 wherein the microstructure contains chromium, zirconium and manganese in a uniform dispersion precipitated throughout the matrix.

6. An alloy according to claim 1 containing a material selected from the group consisting of titanium up to 0.10 percent, vanadium up to 0.15 percent, iron up to 0.60 percent, copper up to 0.30 percent, zinc up to 0.50 percent, boron up to 0.008 percent, and others each 010 percent max., total 0.50 percent max.

7. A hot worked aluminum base alloy having high strength and high impact properties consisting essentially of silicon from 0.3 to 1.3 percent, magnesium from 0.3 to 1.5 percent, chromium from 0.03 to 0.2 percent, zirconium from 0.03 to 0.2 percent, manganese from 0.03 to 0.2 percent, balance essentially aluminum, with the total chromium plus zirconium plus manganese content being from 0.2 to 0.35 percent, wherein substantially all grains are fibrous and grossly elongated containing a plurality of sub-grains, with a length to thickness ratio as extruded of at least 10 to 1, and wherein the microstructure contains chromium, zirconium and manganese in a uniform dispersion precipitated throughout the matrix.

8. An alloy according to claim 7 containing silicon from 0.4 to 0.9 percent.

9. An alloy according to claim 7 containing magnesium from 0.4 to 1.0 percent.

10. An alloy according to claim 7 containing a material selected from the group consisting of titanium up to 0.10 percent, vanadium up to 0.15 percent, iron up to 0.60 percent, copper up to 0.30 percent, zinc up to 0.5 percent, boron up to 0.008 percent, and others each 0.10 percent max., total 0.50 percent max. 

1. A hot worked aluminum base alloy having high strength and high impact properties consisting essentially of silicon from 0.3 to 1.3 percent, magnesium from 0.3 to 1.5 percent, chromium from 0.03 to 0.40 percent, zirconium from 0.03 to 0.20 percent, balance essentially aluminum, wherein substantially all grains are fibrous and grossly elongated, with a length to thickness ratio as extruded of at least 10 to 1, wherein said elongated grains contain a plurality of sub-grains.
 2. An alloy according to claim 1 containing silicon from 0.4 to 0.9 percent.
 3. An alloy according to claim 1 containing magnesium from 0.4 to 1.0 percent.
 4. An alloy according to claim 1 containing manganese from 0.03 to 0.4 percent.
 5. An alloy according to claim 4 wherein the microstructure contains chromium, zirconium and manganese in a uniform dispersion precipitated throughout the matrix.
 6. An alloy according to claim 1 containing a material selected from the group consisting of titanium up to 0.10 percent, vanadium up to 0.15 percent, iron up to 0.60 percent, copper up to 0.30 percent, zinc up to 0.50 percent, boron up to 0.008 percent, and others each 0.10 percent max., total 0.50 percent max.
 7. A hot worked aluminum base alloy having high strength and high impact properties consisting essentially of silicon from 0.3 to 1.3 percent, magnesium from 0.3 to 1.5 percent, chromium from 0.03 to 0.2 percent, zirconium from 0.03 to 0.2 percent, manganese from 0.03 to 0.2 percent, balance essentially aluminum, with the total chromium plus zirconium plus manganese content being from 0.2 to 0.35 percent, wherein substantially all grains are fibrous and grossly elongated containing a plurality of sub-grains, with a length to thickness ratio as extruded of at least 10 to 1, and wherein the microstructure contains chromium, zirconium and manganese in a uniform dispersion precipitated throughout the matrix.
 8. An alloy according to claim 7 containing silicon from 0.4 to 0.9 percent.
 9. An alloy according to claim 7 containing magnesium from 0.4 to 1.0 percent. 